This invention relates to carbinol-containing polyimide oligomers terminated with selected epoxide-reactive groups and to the reaction products thereof with polyepoxides.
Polyepoxides are thermosetting resins which can be cured at reasonably low temperatures with little or no by-product formation. They are viscous liquids or brittle solids which are noted for low shrinkage, lasting adhesion, high dieletric strength and chemical resistance; however, they lose strength at high temperatures. They are useful as coatings, adhesives, or molding compounds.
Polyimides are synthetic organic resins characterized by repeating imide linkages in the polymer chain. They are noted for their outstanding chemical and physical properties, particularly their high temperature oxidative stability and strength. They are likewise useful as coatings, adhesives, and composites. Most polyimides, especially the preferred aromatic polyimides, are extremely difficult to process due to their extremely high softening points as well to their insolubility in organic solvents.
Various methods have been used to insure processibility, such as the use of the polyamic acid intermediates or low molecular weight polyimides terminated with unsaturated polymerizable groups. The solubility has been improved by the use of selected carbinol-containing polyimides, as disclosed in European patent application No. 82401866.7 filed Oct. 11, 1982 and published under No. 0 077 718 on Apr. 27, 1980 and in U.S. Pat. No. 4,489,185 issued to J. E. Schoenberg on Dec. 18, 1984.
Polyimides have been combined with polyepoxides and crosslinked with or without typical epoxy catalysts such as amines or anhydrides. The carbinol-containing polyimides described in the above European patent application have also been combined with a polyepoxide (see Example 18) and cured to an insoluble, infusible state by evaporating off the solvent and heating for 30 minutes at 190.degree. C. The problem with these prior art combinations is that the two part systems are frequently mutually incompatible and the curing reaction which takes place between the polyimide and the polyepoxide is poorly controlled.
There is a need for a polyimide-polyepoxide adduct with improved processibility (e.g., good solubility in organic solvents) and an intermediate Tg.